A considerable challenge in modern synthetic chemistry is the selective direct functionalization of unactivated carbon-hydrogen (C—H) bonds and carbon-carbon (C═C) double bonds (e.g., olefins) (R. G. Bergman, Nature 446, 391 (2007); H. Pellissier, Tetrahedron 64, 7041 (2008)). Adapting asymmetric catalytic processes to these reactions has important consequences in the stereoselective and regioselective elaboration of molecules for natural product and pharmaceutical synthesis. In recent years, much success has been achieved in the development of catalysts for the select addition of oxygen into molecules (M. S. Chen et al., Science 318, 783 (2007)). More challenging is the direct introduction of new carbon-carbon centers into complex structures. A contemporary catalytic approach uses metallocarbenoid intermediates that transfer a reactive carbene into select C—H and C═C bonds, creating new asymmetric highly substituted carbon centers and cyclopropanes, respectively (H. M. L. Davies et al., Chemical Reviews 103, 2861 (2003)). However, the most successful catalysts to date often utilize expensive and possibly toxic transition metal complexes, with dirhodium species marking representative examples. Notably, high yield, regioselectivity, and stereoselectivity in these systems remains difficult to achieve and many of these catalysts are hampered by harsh reaction conditions including high temperature and organic solvents.
The asymmetric cyclopropanation of olefins with high-energy carbene precursors is a hallmark reaction that generates up to 3 stereogenic centers in a single step to make the important cyclopropane motif, featured in many natural products and therapeutic agents (H. Lebel et al., Chemical Reviews 103, 977 (2003)). Limited to using physiologically accessible reagents, Nature catalyzes intermolecular cyclopropane formation through wholly different strategies, typically involving olefin addition to the methyl cation of S-adenosyl methionine or through cyclization of dimethylallyl pyrophosphate-derived allylic carbenium ions (L. A. Wessjohann et al., Chemical Reviews 103, 1625 (2003)). As a result, the diverse cyclopropanation products that can be formed by metallocarbene chemistry cannot be readily accessed by engineering natural cyclopropanation enzymes. As such, there is a need in the art for novel reagents and catalytic schemes that are capable of creating the cyclopropane motif with high yield, regioselectivity, and stereoselectivity, but without the toxicity and harsh reaction conditions associated with current approaches. The present invention satisfies this need by providing novel iron-heme-containing enzyme catalysts for producing cyclopropanation products in vitro and in vivo, and offers related advantages as well.